How do the polar bears cope with the extreme climate conditions in the North Pole

The rare metabolism makes it possible to survive in the cold, the white fur actually helps to cope with the heat

The polar bear's adaptation mechanisms to extreme cold conditions have long been a source of amazement among scientists. These mechanisms allow the bear to live twenty years or more in the Arctic Circle's glaciers, where the temperature reaches minus 45 degrees Celsius.

The white bear is equipped with a double layer of fur, under which there is about 10 centimeters of fat. This way heat loss is almost completely avoided. In addition, it has wide, feathery paws that are used as skis, short and strong claws that are used to grip the ice, and a long snout that allows it to dig holes in the ice and to extract seals from them - the main animal, and almost the only one, that the polar bears feed on. This snout also allows bears to smell prey from a distance of about 30 kilometers. "It's just unbelievable," said Dr. Scott Schleive, head of the polar bear project at the U.S. Fish and Wildlife Service's Anchorage, Alaska branch. "If the body of an animal washes ashore, it's like a bell ringing calling for dinner: the polar bears suddenly appear out of nowhere."

In addition to the discoveries of these impressive adaptive mechanisms, a handful of scientists studying the biology and behavior of the polar bear are now revealing interesting details about the huge, white-furred animal. The researchers discovered, for example, that adult male bears play with each other for hours on end, a highly unusual behavior among adult animals. They stand up on their hind legs and wrestle with each other. They clamp their mouths together. They hug. They look like they are dancing. They fall to the ground side by side in breaks, get up, and go back to frolic. It is a gentle, friendly game and completely opposite in spirit to the violent confrontations between the males during the breeding season, six months later.

What surprises researchers even more than the game itself is the timing in which it takes place. The bears do this at an improbable time - right after the long summer fast, when they are weak and hungry and according to logic should conserve calories and not waste them on physical activity.

"The big question is why they do it," says Dr. James Roth, a biologist at the University of Central Florida in Orlando. The scientists are now looking at several possible explanations for the phenomenon. The males may be establishing a hierarchy of control, or they may be getting into shape after months of inactivity, or they may be making alliances and forming friendships.

Another finding that the researchers discovered is that the bears can quickly go from a normal physiological state to partial hibernation, and vice versa. In the summer months, when the arctic ice recedes and the polar bears have no base from which to hunt seals, they migrate to land, eat almost nothing, and sink into a state known as "walking hibernation": their heart rate slows, their body temperature drops and they stop defecating.

Unlike black bears, for example, which go from hibernation to awakening gradually, over a few weeks, the polar bear doesn't need much more than a happy chance event to radically change its internal systems regulation. "A polar bear can be in 'walking hibernation,' but if it finds carrion, its metabolism immediately kicks back into high gear," says Dr. Ian Sterling, a scientist with the Canadian Wildlife Service in Edmonton. "This is a brilliant adaptation - instead of being dependent on the grace of the calendar, the bears are able to change their physiological state according to needs and luck."

According to Dr. Sterling, high intelligence is required to hunt seals, which are quite intelligent mammals. Despite the poise of the polar bears and their willingness to ambush the seals for long hours near their breathing holes in the ice, the hunt is only successful in 5% of cases. Thus, polar bears excel at conserving energy even at the height of the hunting season. They are able to fall asleep anywhere, in the most amusing positions, using a block of ice as a pillow, and they snooze peacefully while a blizzard covers their entire body except for the tip of their black snout.

In view of the fact that the polar bear does not have abundant food, biologists are disturbed by recent evidence that the bears' survival is becoming more difficult due to global warming. According to Dr. Sterling and his colleagues, because the Arctic ice is melting earlier than before, polar bears in Hudson Bay are forced to come ashore and start fasting two and a half to three weeks earlier than they did 25 years ago. The scientists fear that although there is no immediate threat to the global population of polar bears, numbering about 30 individuals, subgroups like the one in western Hudson Bay may disappear if the climate continues to warm.

In evolutionary terms, the polar bear is an extremely young animal. According to genetic and biological analyses, it separated from the brown bears no more than 150 thousand years ago, that is, the polar bear is one of the late mammals on Earth, about as young as Homo sapiens. According to Dr. David Petkau, president of the organization "Genetics InternationalWildlife" in British Columbia, the explanation is that the polar bears separated from the brown bears during an ice age and quickly adapted to life in a glacier environment.

Polar bears currently live in the Arctic Circle in Alaska, Canada, Greenland, Norway and Russia. They do not live in the South Pole, and descriptions of polar bears in the company of penguins are nothing more than practicality.

Polar bears are known and loved for their bright white fur. The fur is practically unpigmented. Each of the hairs is a transparent tube, which reflects all wavelengths of light and therefore appears white. According to one theory, the white fur evolved because it allowed bears to blend in with the snow and thus ambush their prey more easily. But the bears hunt in winter, and in winter it's almost always dark. So what is the advantage of the white fur? According to Dr. James Roth, the advantage of the white fur may be that it reduces heat absorption. In the places where the bears stay in the summer, the temperature may reach 32 degrees. "Heat distress is a serious problem for the bears," says Ruth, "and the white fur may help."

In polar bears, like other bears, there is a considerable difference between the size of the mother, which weighs about 250 kilograms, and the size of a day-old cub, which weighs less than 500 grams. "This is a surprising feature of the bear family," says Dr. Petkau. "The gap is beyond the accepted range for mammals with a placenta and closer to that existing in marsupials such as the kangaroo."

A pregnant bear comes ashore in the summer, digs a den for herself in October, and two months later gives birth to one to three cubs. When the mother emerges with her cubs in April, she has not eaten for nine months and has lost 75% of her weight. But unlike humans, for example, bears that lose a lot of weight shed only fat and their muscle tissue is not damaged.

The cubs stay with the mother for a period of up to three years, during which she teaches them to hunt and protects them from adult males, known as cub eaters. But although the cubs need protection, they are not helpless, says Dr. Jane Waterman of the University of Central Florida: "On several occasions I witnessed a situation where a large bear approached two much smaller bears. The little bears stood shoulder to shoulder and forced the big bear to retreat."

Natalie Angier New York Times, courtesy of Walla